In the construction industry, excavations of various types, such as foundations, trenches and the like, are formed in the ground. For example, a trench is often excavated in soil in order to provide access to underground conduits, such as water and sewage pipes, that in turn require maintenance, replacement and/or installation.
Due to unstable soil conditions, improper sloping of an excavation and/or other unaccounted for occurrences, the sidewalls of an excavation can loosen and subsequently collapse. The collapse of an excavation sidewall can result in the destruction of equipment, a delay in job completion and, most seriously, injury or death to professionals who are working within the excavation during the collapse. In response thereto, the Occupational Safety and Health Administration (OSHA) has recognized excavations as extremely hazardous construction operations and, as a result, has promulgated regulations directed to the manner in which excavations are created and to the structures used to support excavations to prevent sidewall collapse.
A trench box one well-known piece of shielding, or shoring, equipment that is commonly used in the construction industry to support the two principal walls of a trench or similar excavation. A trench box is commonly constructed using a pair of enlarged, rigid, metal support panels that are spaced apart and arranged substantially in parallel by a plurality of laterally extending, tubular separation members, which are commonly referred to in the art as spreader bars.
In use, a trench is excavated in the soil to permit access to a particular conduit. The trench box is then driven vertically downward into the trench with the opposing outer panels disposed on opposite sides of the conduit and ultimately in firm contact against the main trench walls, this vertical displacement step being referred to herein simply as the “drive mode.” Positioned in this manner, the planar panels provide a shoring or shielding function by holding the sidewalls of the excavation in place, thereby preventing the sidewalls from collapsing into the trench. With the trench box disposed in place, construction professionals are able to further excavate the trench and readily access a particular section of the conduit through its open top end without the risk of sidewall collapse.
Once treatment of the particular section of the conduit is completed, the trench box is typically dragged longitudinally within the trench to allow for further excavation as well as the similar treatment of adjacent sections of the conduit, this longitudinal displacement step being referred to herein as the “slide mode.” By drawing the trench box longitudinally within the trench in defined increments, or stages, multiple sections of a conduit can be sequentially accessed and treated in a safe manner.
One type of trench box which is well known and widely used in commerce utilizes a pair of enlarged panels that are generally planar in shape. Each panel is typically constructed using a thin, rectangular, steel skin plate that has flattened inner and outer surfaces. A plurality of longitudinal tubular members, often U-shaped or L-shaped in transverse cross-section, is welded onto the inner surface of the skin plate to provide strength, stiffness and structural rigidity to the panel. The longitudinal members are disposed horizontally in a parallel relationship with adjacent members often separated by hollow spacers or channel-like gaps in order to reduce material costs and overall weight. To provide further strength to the panel, a plurality of vertical stiffening members, or stiffeners, is typically welded to the inner surface of the skin plate in a spaced apart relationship. It is to be understood that the longitudinal and vertical members preferably share a common thickness and thereby provide each planar panel with flattened interior and exterior walls that extend in parallel.
For example, in U.S. Pat. No. 7,611,308 to R. Kundel, Sr., the disclosure of which is incorporated by reference, there is provided a panel for supporting the sidewalls of an excavation that includes a plate, longitudinal members and vertical members. Each longitudinal member includes a first leg extending along the length, substantially parallel to and spaced laterally from the plate. The first leg of each longitudinal member is located adjacent and secured to the first leg of another member. A second leg, integral with the first leg, extends along the length, away from the first leg and toward the plate, the second leg being secured to the plate. Axially spaced vertical members are welded to the plate and to the longitudinal members.
Although well-known and widely used in art, trench boxes of the type described above, which rely upon a panel construction that features longitudinal and vertical tubular members that are welded onto the inner surface of a common skin plate, have been found to suffer from a couple notable drawbacks.
As a first drawback, it has been found that trench boxes of the type as described above that utilize planar panels with flattened interior and exterior walls are relatively difficult to move within a trench during either its drive phase or its slide phase. Specifically, the planar construction of each panel maximizes the surface area of the panel that is exposed for contact with the soil during displacement of the trench box. As a result of the increased surface area, the frictional forces imparted onto each panel are similarly increased. Accordingly, the speed in which the trench box can be properly positioned within the trench is limited, thereby resulting in decreased productivity, which is highly undesirable.
As a second drawback, it has been found that trench boxes of the type as described above are incapable of adequately withstanding significant inward lateral forces. In particular, it has been found that each panel tends to inwardly distort, or bow, in response to the considerable lateral load applied thereto by certain types of trench walls (e.g., trench walls formed at a considerable depth and/or with limited soil stability). This permanent inward curvature, or bowing, of the panels renders the distorted trench box considerably difficult to drag longitudinally through a trench during its slide mode. More specifically, the inward bowing of the panels substantially increases the frictional forces imparted on the trench box during its slide mode, thereby resulting in decreased productivity, which is highly undesirable.